The present invention relates to vibration energy absorbing apparatus which absorbs vibration energy such as is produced by wind and/or earthquake in structures such as buildings using a plastic deformation of superplastic material used in the apparatus.
A lead plasticity energy absorbing apparatus using the plastic deformation of lead is known, for example, in Japanese Patent Application laying open No. Sho 48-72941 corresponding to U.S. Pat. No. 3,833,093 and Patent Application laying open No. Hei 2-26332.
According to the former conventional technique, the lead plasticity energy absorbing apparatus includes a cylinder, a rod inserted in the cylinder, and lead enclosed in the space between the cylinder and the rod. When the rod moves relative to the cylinder, the lead passes by radially inward raised portions or reduced inner diameter portions formed on the inner wall of the cylinder and is plastically deformed. By energy consumption on the plastic deformation, the periodic vibration energy is absorbed.
According to the latter prior art, the lead plasticity energy absorbing apparatus includes a hermetically sealed container which has an operating chamber which in turn contains lead and means for preventing the rotation of the enclosed lead, and a shaft which extends through the container of the operating chamber and has raised portions or resistance wings within the operating chamber. The sealed container and the shaft with resistance wings are connected to the corresponding structures which are movable relative to each other such that the container is rotated around the shaft through a link mechanism which converts the relative movement or displacement between the structures to a rotational movement.
Any of these conventional arrangements expects energy absorption by plastic deformation of the lead due to the movement of the raised portions moved in conjunction with the relative displacement of structures.
As a result of study of the characteristics of the conventional energy absorbing apparatus, the applicants have found that since the energy absorbing apparatus employs an arrangement which absorbs energy due to plastic deformation of lead, the axial force acting on the rod in the former case and the torque of the shaft with the wings or fins in the latter case tend to increase compared to respective expected values as well as the axial force or the torque fluctuates and the energy absorbing performance for small amplitude vibrations tends to be greatly reduced.
It was found in these prior art arrangements that when the raised portions plastically deform the lead, the lead is raised ahead of the raised portions in the direction of forward movement to thereby increase the torque on the shaft and that a spacing is formed at the lead behind the raised portions and acts as a dead zone which would impair stabilization of the energy absorption characteristic.